This invention relates to a method and apparatus for elemental analysis. This invention relates more particularly to a method and apparatus with microwave plasma source for monitoring of air and liquid streams for elemental contaminants including transition metals, rare earth elements, actinides, or alkali and alkaline earth elements.
This invention was made with government support under Contract No. W-7405ENG-36 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
Because of increasing global efforts to protect the environment and increasing concerns for worker safety, there is increasing need for capability for real-time monitoring of air and liquid streams for the presence of transition metals, rare earth elements, actinides, or alkali and alkaline earth elements. There is a continuing and increasing need for sensitive, real-time, portable monitoring devices for detection of the presence of elements in industrial waste streams.
In one particular example, beryllium is extracted from beryl ore and converted to beryllium hydroxide for the production of metal alloys, oxides, ceramics, and pure beryllium for use in various industries and military applications. Because of increased regulatory activity and awareness of health hazards during extraction and production of beryllium and during industrial and commercial use of beryllium products, it is important to be able to accurately evaluate workplace explosures in a timely manner.
Several methods of monitoring air for the presence of beryllium or other trace elements have been developed.
High volumes of air for sampling can be drawn through filters at high flow rates. After ranges of time from minutes to hours, the filters can be taken off location for laboratory analysis.
Inductive plasma spectrometry has been used to analyze elements from a plasma produced by application of an electromagnetic field to a plasma gas; see e.g., U.S. Pat. No. 4,844,612 (Durr and Rozain, Jul. 4, 1989).
Microwave plasmas have been used for trace element monitoring. Microwave plasmas sustained in a portion of an undiluted furnace exhaust flow have been used for continuous emission monitoring for trace metals in furnace exhaust by atomic emission spectroscopy. These waveguide devices are constructed of refractory materials compatible with high-temperature environments and are mountable inside the furnace exhaust ducts. See, e.g., U.S. Pat. No. 5,671,045 (Woskov, et al., Sep. 23, 1997) which is a continuation of U.S. Pat. No. 5,479,254.
Fused quartz fiber optics in close proximity to a plasma flame have been used to transmit UV through visible emissions to three spectrometers for simultaneous monitoring of several metals. This is disclosed in Woskov, P. P., D. Y. Rhee, P. Thomas and D. R. Cohn, xe2x80x9cMicrowave plasma continuous emissions monitor for trace-metals in furnace exhaust,xe2x80x9d Rev. Sci. Instrum., 67 (10), Oct. 1996, American Institute of Physics).
Several methods of monitoring liquid streams have been disclosed in the literature. These include introduction of vapors generated from liquids to be sampled into inductively coupled plasma source atomic emission spectrometers for analysis.
However, there is still a need for sensitive, real-time, portable monitoring devices for detection of the presence of elements in ambient air and liquid streams and a need for economical, energy-efficient monitoring devices.
Therefore, it is an object of this invention to provide an apparatus and method for analysis of air or liquid streams for presence of various elements.
It is another object of this invention to provide such an apparatus and method particularly for sensitive, real-time, on-site monitoring of air for the presence of beryllium.
It is a further object of this invention to provide a reliable, low-energy microwave plasma monitoring apparatus and method.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims which are intended to cover all changes and modifications within the spirit and scope thereof.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, there has been invented a process for analyzing ambient air or other gas samples, in a microwave powered plasma torch without use of an additional carrier gas. There has also been invented an apparatus for analyzing ambient air, other gas samples, or nebulized and desolvated liquids wherein a novel arrangement of plasma gas and sample gas conduits is used to enhance dependability of the plasma. This apparatus embodiment of the invention has a concentric arrangement of plasma gas and sample gas conduits so as to provide a sheath of plasma gas both within and on the outside of the flow of sample air into the plasma region.
The multiple conduit apparatus of the invention comprises:
(a) a sample gas conduit positioned to conduct a flow of a sample gas to a plasma region;
(b) a first plasma gas conduit coaxially positioned within the sample gas conduit;
(c) a second plasma gas conduit positioned such that the sample gas conduit is within the second plasma gas conduit;
(d) a microwave energy source sufficient to generate a plasma in the plasma region;
(e) a microwave transmitter connecting said microwave energy source to the second plasma gas conduit; and
(f) analytical instrumentation connected to receive signals from the plasma region.
The microwave plasma torch can either be contained within a sealed housing or can be operated in ambient air at ambient pressures.
The microwave plasma torch of this invention can be operated continuously for real-time analysis of air.
The apparatuses and methods of the present invention can be used wherever there is a need for monitoring air for the presence of minor amounts of elements, particularly transition metals, rare earth elements, actinides, and alkali and alkaline earth elements. The invention apparatus can also be used to monitor for the presence of halogens, sulfur and silicon. The invention apparatuses and methods are more particularly useful for monitoring air for the presence of beryllium.